PNEUMATIC TOOLS comprise various classes of hand tools which are operated by compressed air power. They are di vided in two general classes according to the principle of operation (I) percussion, (2) reciprocating motor-driven. Under percussion tools are grouped rivetting, chipping and sand rammers, pneumatic diggers, rock drills, paving breakers, etc. ; each using a piston or plunger for striking a blow. Reciprocating motor-driven tools employ a reciprocating piston air motor to drive a spindle from which power can be used for drilling, grinding, etc. The tools under this classification include pneumatic drills, grinders, motors, hoists, etc. Pneumatic tools usually operate best when supplied with compressed air at 90 lb. gauge pressure.
The principal uses of pneumatic tools occur on those classes of work where it is not possible or not advisable to take the work to a machine. A pneumatic tool, being a self-contained power unit, can be taken to the work and various operations performed rapidly, with a minimum of manual labour. Pneu matically operated tools are suited for a wide variety of uses because of their availability, the adaptability of compressed air power, the absence of danger and because they embody within small confines a great range of power and action. Other ad vantages are rugged construction, simplicity, and easy operation.
are made in a variety of sizes and types, and the name for each is governed largely by the work to be performed. This group covers chipping, rivetting, scaling and caulking hammers, diggers, paving breakers, rock drills and the like implements. (See BLASTING.) Each class of work requires a hammer of a particular size, weight, speed and strength of blow. In the operation of most rivetting hammers air enters the hammer at the air inlet in the handle, the amount of air being con trolled by the throttle valve which is actuated by a trigger. After passing the throttle valve the air is conducted through the passage in the handle to the valve chamber containing the operating valve and valve box. The valve is moved back and forth in the valve box by the action of the air pressure on its differential areas. As the valve moves forward it admits air back of the piston, throwing it forward against the rivet set, which forms the rivet head. The piston, after striking a blow, is returned for another stroke by air admitted to the front of the cylinder, which is covered by the piston in this position. Hammers for chipping, caulking and scal
ing are very similar in construction to the rivetting hammer. The chipping hammer is used to clean foundry castings, for caulking the seams of boilers and tanks, pipe joints, etc., saving two-thirds the time required by hand work.
have a long barrel containing a piston having a projecting rod at one end, to which the tamping butt is attached. In action the piston moves rapidly up and down in the barrel lifting the tamping butt from the sand and returning it with considerable impact against the material to be rammed. The ramming of certain classes of moulds in foundry work, a long and arduous task when done by hand, is rapidly accomplished by means of the pneumatic sand rammer. Machine-rammed moulds are harder and more uniform than those rammed by hand, resulting in better castings. Floor rammers are used for working on large moulds on the floor, and the bench rammer on small bench moulds. These tools strike up to Boo blows per minute. The force and number of blows are regulated by the operator with a throttle. The sand rammer is also used to tamp the back-fill in trenches in city streets, where it is desired to pack the sand solidly and by this means avoid the subsequent set tling.
Drills.—Portable pneumatic drills are divided into four general types : the reversible drill, the non-reversible drill, the woodborer and the close-quarter drill. The several types are also given certain other minor divisions according to the use to which they are put, such as boring, reaming, tapping, flue rolling and stud-setting. The larger sizes of pneumatic drills use a four-cylinder V-type air motor, with one crank throw pro vided for each pair of cylinders in the same cross plane. The power from the crank-shaft is transmitted to the drilling spindle by gears arranged to give the spindle speed desired. A feed screw with a feed handle is used to feed the drill up to the work. A main valve, of rotary type, controls the supply of air to each of the four cylinders, the air supply reaching this main valve through a throttle handle. At the upper end of the main valve is located a centrifugal speed governor which limits the speed of the drill motor after it has passed the point of maximum horse power.